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5.2 10BASE-T Components

10BASE-T Link Integrity Test

10BASE-T MAUs continually monitor the receive data path for activity as a means of checking that the link is working correctly. When the network is idle, the MAUs also send a link test signal to one another to verify link integrity. Vendors can optionally provide a link light on the MAU; if the link lights on both MAUs are lit when you connect a segment, then you have an indication that the segment is wired correctly.

It's important that both link lights, one at each end, be lit. That indicates that there is a correctly wired signal path between both devices. On the other hand, the presence of the link lights merely means that the segment is correctly wired. Since the link test pulse operates more slowly than actual Ethernet signals, the link lights are not always a guarantee that Ethernet signals will work over the segment. Odds are good that a correctly wired segment will work, but if the signal crosstalk on the segment is too high, then it may not work despite the presence of the link lights.

Quick Reference Guide to 10BASE-T Twisted-Pair Ethernet - 04 SEP 95
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